Asian Ancestors Had Sex with Mysterious Human Cousins

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Neanderthals weren't the only ancient cousins that humans
frequently mated with, according to a new study that finds that
East Asian populations share genes with a mysterious archaic
hominin species that lived in Siberia 40,000 years ago.

This group, the Denisovans, is known only by a few bone
fragments: A finger bone, a tooth and possibly a toe bone, which
is still undergoing analysis. The Denisovans likely split off
from the Neanderthal branch of the hominin family tree about
300,000 years ago, but little else is known about their
appearance, behavior or dress. But just as researchers have
learned that ancient
humans and Neanderthals mated, they've also found
genetic echoes of the Denisovans in modern residents of
Pacific islands, including New Guinea and the Philippines.

The new research expands the Denisovan genetic influence,
uncovering Denisovan genes in modern East Asian populations. The
genetic signal is less strong than it is in the Oceanic islands
such as the Philippines, said study researcher Mattias Jakobsson,
a professor of evolutionary biology at Uppsala University in
Sweden. On the Asian mainland, the genetic similarities to
Denisovans are strongest in southern China and Southeast Asia.

"We are actually finding gene flow in Southeast Asia," Jakobsson
told LiveScience. "So it's not restricted to the Oceanian parts
of the world."

Jakobsson and his colleagues first ran complex computer
simulations of genetic data to understand how the limited gene
information collected in population genetics research, which
includes just segments of DNA, might be biased. With that
understanding, the group then examined genetic data from more
than 1,500 modern humans from all over the world.

Comparing that modern data with the Denisovan genome revealed
that Asians, especially Southeast Asians, have a higher
proportion of Denisovan-related gene variants than other world
populations except for the Oceanic islanders. While Oceanians
have about a 5 percent fraction of Denisovan-related ancestry,
Southeast Asians have around 1 percent, the researchers report
today (Oct. 31) in the journal Proceedings of the National
Academy of Sciences. In comparison, genes from modern non-African
humans have about a 2.5 percent fraction of
Neanderthal ancestry.

It's hard to tell when the Denisovan and human interbreeding
occurred, Jakobsson said, but since Europeans don't have
Denisovan ancestry, it's likely the mating occurred around 23,000
to 45,000 years ago, after Southeast Asians and European
populations diverged.

Jakobsson and his colleagues are working on further studies on
early human genetics and the steps that led to the
modern human genome. The more digging scientists do, the more
complex the genetic picture becomes, he said. Notably, bits of
genes are almost all that are left behind of some ancient
populations, including the Denisovans, he said.

"We don't really know what they looked like, how they behaved or
anything like that," Jakobsson said. "It's really genetics that
gives us an edge here."